The present disclosure relates to a toner conveying device used in an image forming apparatus such as a copy machine, a printer, a facsimile, a multifunctional peripheral having functions of these apparatuses, or the like.
A conventional image forming apparatus generally performs a process in which a powdered developer is mainly used to visualize, by use of a developing device, an electrostatic latent image formed on an image bearing member such as a photosensitive drum or the like, and a visualized image (toner image) thus formed is transferred onto a recording medium and then is subjected to fixing processing. Toner remaining on the surface of the image bearing member is removed by a cleaning device, after which a new toner image is formed thereon. The residual toner that has been removed by the cleaning device is stored in a waste toner bottle. When the waste toner bottle becomes filled to capacity after a predetermined number of times of printing, a user is notified as such, and the waster toner bottle is discarded to be replaced with a new one.
It has been known to use, as a waste toner collecting path from the cleaning device to the waste toner bottle, a toner conveying path constituted by a pipe-shaped conveying passage including inside thereof a conveying screw. In this toner conveying path, in a case where, due to dimensional tolerances on the outer diameter of the conveying screw and on the inner diameter of the conveying passage, warping of the conveying screw, or the like, a trajectory of an outer peripheral edge of the conveying screw when rotating becomes larger than the inner diameter of the conveying passage, an excessive rotational load might be generated by friction to stop the conveying screw from rotating. In order to avoid this, typically, dimensional setting is so performed that the outer diameter of the conveying screw is smaller than the inner diameter of the conveying passage.
Such dimensional setting, however, brings about a situation where, due to a clearance (gap) present between the conveying screw and the conveying passage, the conveying screw, if warped, rotates while swinging in a radial direction (while being decentered) and impacts against an inner surface of the conveying passage, resulting in occurrence of a hitting sound.
To be more specific, if the conveying screw is warped, when a warping direction is downward, the conveying screw sags under its own weight in the same direction as the warping direction and thus is deformed in an increased amount. On the other hand, when the warping direction is upward, the conveying screw sags under its own weight in a direction opposite to the warping direction and thus is deformed in a decreased amount. Because of this, when the conveying screw rotates from a state where it is warped upward, the conveying screw is gradually shifted in direction from a direction in which the conveying screw is in a balanced state where a deformation amount thereof is small to a direction in which sagging thereof under its own weight acts to increase the degree of the warping thereof. As a result, the conveying screw rotates while being deformed into a large wave shape and impacts against the inner surface of the conveying passage. The level of a hitting sound that occurs at this time increases with increasing degree of warping of the conveying screw, with increasing size of the clearance (gap) between the conveying screw and the inner surface of the conveying passage, and with increasing weight of the conveying screw.
As a solution to this, there has been known a toner conveying device that has a portion where the outer diameter of a spiral-shaped protrusion (spiral vane) of a conveying screw comes in extreme proximity to the inner diameter of a cylindrical conveying passage so that the conveying screw can rotate stably while being in contact at part of the outer diameter thereof with an inner side of the cylindrical conveying passage. Furthermore, there has also been known a toner conveying pipe that is composed of a pipe main body having a semi-tubular portion and a semi-tubular lid that is joined to the semi-tubular portion and in which a joint surface between the pipe main body and the semi-tubular lid is made substantially flat, and ultrasonic welding is performed with respect to a joint portion therebetween, so that excellent air tightness and dimensional accuracy are achieved.
In the above-described configuration, however, due to dimensional tolerances and assembly tolerances of components, there is a limitation in setting a clearance between the conveying screw and the cylindrical conveying passage, and if the conveying screw is warped beyond the size of the clearance, the conveying screw impacts against the inner surface of the conveying passage, making it impossible to reliably prevent a hitting sound from occurring. Furthermore, in the method in which there is provided a portion where the outer diameter of the conveying screw comes in extreme proximity to the inner diameter of the cylindrical conveying passage, part of the spiral vane of the conveying screw rubs against the inner surface of the conveying passage, so that the rotational load is increased. Moreover, the presence of toner in the clearance between the conveying screw and the conveying passage further increases the rotational load, so that the flowability of the toner is decreased due to frictional heat to deteriorate conveying efficiency, and the toner might even be solidified if left in that state for a long period of time.
The foregoing has described the problems with the case where a toner conveying path constituted by a pipe-shaped conveying passage including inside thereof a conveying screw is used as a waste toner collecting path from a cleaning device to a waste toner bottle. In addition, similar problems arise in a case where a toner cartridge for replenishing a developing device with toner is incorporated, and a toner conveying path constituted by a conveying pipe including inside thereof a conveying screw is used also as a toner replenishing path used to replenish the developing device with toner from the toner cartridge depending on a toner consumption in the developing device.